The present invention relates to a method and apparatus for automatically identifying the location of a vehicle.
Various systems are known in the art for automatically locating a plurality of fleet vehicles, such as taxi cabs, police cruisers, etc. over the relatively large area serviced by the fleet of vehicles. In a system described in the patent to Chisolm, U.S. Pat. No. 3,419,865, the location of each vehicle is determined by triangulating its location with distance information obtained by reception of its radio signal by plural spaced receivers. Other systems, however, include a plurality of wayside stations distributed throughout the service area, where each station automatically communicates a location-identifying signal to vehicles passing nearby. Each vehicle automatically retransmits the location-identifying signal to a central station. The central station then logs that vehicle as being at the identified location at that time.
One of the difficulties with the latter type of system resides in the cost and reliability of the short range communication links between each wayside station and nearby vehicles. Often, the wayside stations communicate the location-identifying signals to the passing vehicles by means of short range radio transmitters. Patents disclosing systems of this sort include Haemmig, U.S. Pat. No. 4,083,003 and Ross et al., U.S. Pat. No. 3,757,290. In another system, disclosed in Christ, U.S. Pat. No. 3,697,941, the location-identifying information is communicated to the vehicles by means of modulated light energy.